Heated respiratory therapy humidifier

ABSTRACT

A humidifier assembly is disclosed. Parts of the humidifier assembly may be disposable. The assembly comprises a housing, heater means on the housing, a liquid water supply means that communicates with the heater means, a hollow shell on the housing that defines a humidification chamber, and a filter means in the humidification chamber and positioned in juxtaposition with the surface of the heater means for passing water vapor into breathable gas. Preferably the filter means is hydrophobic.

This is a division of application Ser. No. 496,103, filed May 19, 1983,now U.S. Pat. No. 4,532,088.

BACKGROUND OF THE INVENTION

Several types of humidifying devices are presently available for addinghumidity and heat to a breathable gas stream supplied to patientsutilizing ventilators or undergoing inhalation therapy. Also, becausesome such patients have reduced breathing capability, each breath may besupplied mechanically directly to the trachea. However, when the naturalmembranes in the nose and mouth are bypassed, artificial humidificationis required.

Existing systems for humidifying a breathable gas stream have one ormore disadvantages. For example, systems of the type shown in U.S. Pat.No. 4,110,419 require a large sterile reservoir, usually disposable,which is not only expensive but also contributes greatly to pressurecompliance of the system. Thus, the pre-filled, sterile water reservoirsexpand and contract with the ventilator pressure. Further, a supply ofsuch reservoirs takes up a great deal of storage space. Sterile water isalso expensive, it sells for as much as several dollars a quart. Theseand other disadvantages are overcome or at least substantially minimizedby the present invention.

SUMMARY OF THE INVENTION

The present invention provides an improved humidifier assembly forenhancing the moisture content of a breathable gas to be inhaled by apatient undergoing inhalation therapy. The humidifier assembly comprisesa compact housing, and a special heater means and a hollow shell bothmounted on the housing. The heater means has a generally horizontallydisposed heater surface adapted to receive liquid water from a suitableliquid water supply in a direct heat transfer relationship. The hollowshell defines a humidification chamber and an inlet for a breathablegas. An outlet for humidified breathable gas is also provided.

The humidification chamber is in juxtaposition with respect to theheater surface. Liquid water from the liquid water supply may beconveyed to the heater surface for vaporization of said liquid water inthe humidification chamber. Preferably the heater means projectsupwardly into the humidification chamber so that the gas to behumidified sweeps past the heater surface on which water vaporization iseffected. A filter assembly through which water to be added to thebreathable gas passes is positioned between the liquid water supply andthe humidification chamber.

In a preferred embodiment the filter assembly includes a relativelyhydrophobic filter which is disposed closely adjacent the heater surfacewith liquid water being supplied to the heater surface from below thefilter assembly so that only water vapor passes upwardly therethroughand into the humidifier chamber.

Further objects, features and advantages of this invention will becomeapparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, in cross-section, illustrating ahumidifier assembly embodying this invention;

FIG. 2 is a plan view of a filter base assembly utilized in a preferredembodiment of this invention;

FIG. 3 is a fragmentary sectional elevation of the filter base assemblytaken along plane 3--3 in FIG. 2;

FIG. 4 is a plan view of a hollow shell that defines the humidificationchamber and fits over the filter base assembly shown in FIGS. 2 and 3;and

FIG. 5 is sectional elevation of the hollow shell taken along plane 5--5in FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention can be practiced and used in many different forms. Thespecification and accompanying drawings disclose specific embodimentsthat illustrate the invention. This invention is not intended to belimited to the specific embodiments illustrated, however.

Housing 10 supports an upstanding, pedestal-like heater means 14 and anassociated humidification chamber 16 defined by hollow shell 15 fittedonto housing 10. Temperature control knob 12 is also mounted on housing10.

The heater means 14 defines a liquid water passage 13 which is connectedto and communicates with water supply inlet nozzle 25 by means offlexible conduit 24. Water can be supplied to inlet nozzle 25 in anysuitable manner, such as from an external liquid water source, e.g., anassociated reservoir (not shown). Nozzle 25 can also be in the form of acannula or spike adapted to penetrate a sealing membrane of a waterbottle that serves as the external liquid source.

Shell 15 includes a downwardly depending sleeve portion 17 which,together with hollow skirt portion 18, defines a central cavity 19 inwhich heater means 14 is positioned. Sleeve portion 17, via a seal, suchas an "O" ring 11, sealingly surrounds the heater means 14 and permitsthe interchange of the hollow shells such as shell 15. Skirt portion 18terminates in an inwardly extending flange 21 which supports a filterelement 46, preferably a hydrophobic filter element, so that itconfronts the associated upper surface of the heater means. Tofacilitate the distribution of liquid water thereover, the upper heatersurface can be provided with a slight crown, but it is not essential todo so. When filter element 46 is hydrophobic, only water vapor can passupwardly therethrough.

Shell 15 further defines a gas inlet 28 and a humidified gas outlet 20.Vent 23 communicates with the external associated liquid water sourceand provides pressure equalization therewith as well as flow control aswill be discussed below.

In use, in the humidifier assembly of FIG. 1 water is flowing from waterinlet 15 upwardly to hydrophobic filter 46. As the water passes upwardlythrough passage 13 it is preheated by the action of resistance heatingelement 22. If the heater means is operated at a relatively hightemperature so that too much heat is transferred to the liquid water inpassage 13, this passage may be partially insulated by a sleeve, e.g., atetrafluoroethylene tube, that limits the rate of heat transferthereacross. The upper heated surface of heater means 14 evaporates thewater distributed thereon, while liquid water entry into the chamber 16is precluded. Water vapor, however, is freely transmitted upwardly intohumidification chamber 16 through filter 46 for humidification of thedry breathable gas. Optionally, a wicking layer 54 can be providedbetween heater means 14 and the hydrophobic filter 46. The wicking layeror the filter can be used to control water flow rate to the heatermeans, if desired.

Liquid level back-up control in the event of filter rupture isaccomplished by vent 23 which, when occluded by water, prevents ventingand therefore prevents liquid flow from the external reservoir (via thewater inlet) to the heater means 14. Again, it is not necessary to usesterile water since the pore size of filter 46 can be selected so as toexclude contaminants such as bacteria from the humidification chamber.Distilled water, or even tap water, may be used.

A preferred embodiment of the present invention is illustrated in FIGS.2 through 5, inclusive. Referring to FIGS. 2 and 3 in particular, filterbase assembly 130 that can be removably positioned over heater 114includes base flange 132 unitary with upstanding skirt portion 118 andinwardly extending peripheral flange 121. Hydrophobic filter element 146is mounted in filter base assembly 130 at flange 121 and at juncture 134of radially extending filter retaining members 136 that connect withperipheral flange 121. Nipple 138 projects from juncture 134 and extendsinto the heater-receiving cavity defined by skirt portion 18.

Heater 114 is provided with a relatively flat, substantially horizontalupper surface or plateau adapted to receive and distribute liquid water.Additionally, heater 114 defines central passageway 113 thatcommunicates with an external liquid water supply via conduit 124adjacent to the upper surface of heater 114. A peripheral protuberance140 extends into passageway 113 from heater block 146 and defines avalve seat for a check valve such as ball valve 142 situated withinpassageway 113.

Ball valve 142 is lighter than water, i.e., it has a specific gravityless than one, preferably about 0.4 to about 0.6. Thus, when an aliquot144 of liquid water is present in passageway 113, the buoyancy of waterurges ball valve 142 against the valve seat defined by peripheralprotuberance 140 if the filter base assembly 130 is not in place,thereby precluding liquid water spillage. On the other hand, when filterbase assembly 130 is positioned over heater 114, nipple 138 abuts ballvalve 142 and is sufficiently long to prevent ball valve 142 fromsealing passageway 113, thereby permitting liquid water flow to theupper surface of heater 114 and to hydrophobic filter 146. In analternative embodiment the ball valve can be heavier than water, inwhich event ball valve is urged against the valve seat by means of abiasing spring.

In either case, the check valve can be incorporated as part of theheater means, or the check valve can be made as a separate sub-assembly,e.g. within a tube of a relatively heat-resistant material which tube isthen positioned within passageway 113 as a unit. In the latter instance,protuberance 140 can be made integral or unitary with the inserted tubeas desired.

Circumferential O-ring 111 provides a liquid-tight seal between heater114 and the inner surface of skirt portion 118. Resistance heaterelement 122 in heater block 146 provides the desired energy input tovaporize the required amount of liquid water.

Shell 115 (FIGS. 4 and 5) defines the humidification chamber and isprovided with side outlet port 120 and top inlet port 128. Additionally,vent nozzle 123, serving the same function as nozzle 23 described abovein connection with embodiment illustrated in FIG. 1, is provided onshell 115. Preferably, a hydrophobic filter element 152 is providedacross the venting port 150 for nozzle 123.

The lower rim 154 of sleeve portion 117 is received in groove 156defined in base flange 132. Shell 115 can thus be mounted onto filterbase assembly 130 to provide a humidification canister. If it is desiredto provide a complete, disposable canister in a sterile package, thelower rim 154 of shell 115 is permanently bonded to base flange 132. Inthe alternative, shell 115 can be sterilizable and thus non-disposable,and only filter base assembly 130 can be a disposable item. In thelatter case, rim 154 is removably received into groove 156. If desired,rim 154 and base flange 132 can be provided with mating threads or abayonet-type interlock to removably secure shell 115 to filter baseasembly 130.

In a yet another variant, filter element 146 can be provided with aseparate peripheral frame that is removably attachable, e.g. by means ofthread or lugs, to skirt portion 118 and thus is independentlyreplaceable as required. In such an event, shell 115 and filter baseassembly can be sterilizable and thus non-disposable and can bepermanently or removably joined to one another.

The overall operation of the humidifier illustrated in FIGS. 2 through5, inclusive, is substantially the same as that described hereinabovefor the embodiment of FIG. 1. However, the preferred embodiment shown inFIGS. 2 through 5 further provides the liquid water flow interruptfeatured by the coaction of nipple 138, and a check valve that includesvalve seat 140 and ball valve 142.

While any heat-resistant filtering material can be used for filters 46and 146 as long as the pore size selected is sufficient to preventundesirable contaminants from entering the humidification chamber, theuse of a hydrophobic filter material is preferred. When a hydrophobicfilter material is used, only water vapor can enter the humidificationchamber and the entrainment of water droplets by the gas stream passingthrough the chamber is avoided. Additionally, a hydrophobic filtermaterial provides a convenient means for controlling the flow of liquidwater to the upper heater surface for vaporization as well as forelimination of any air bubbles trapped between the filter and theadjacent heater surface.

Hydrophobic filter materials suitable for present purposes are availablecommercially. For use in humidifiers embodying the present invention apore size of about 0.02 to about 0.5 micrometers (μm is preferred;however, the pore size can be smaller or larger, as desired, dependingon the potential contaminants that are to be excluded and the filterflow-through rate that is desired.

Particularly preferred filter materials for use in the filterscontemplated by the present invention are microporous expandedpolytetrafluoroethylene structures having a matrix of nodulesinterconnected with fibrils. Alternatively, membrane filters that areinherently hydrophobic or fibrous mats treated with a water repellentsubstance can be used.

The degree of porosity of the filter material can be selected to meetthe contemplated throughput requirements. Preferably the porosity issuch as to be capable of providing a flow rate equivalent to about 1-5liters of air per minute per square centimeter as a pressure of about 10pounds per square inch (about 0.7 kilograms per square centimeter).

The foregoing discussion and illustrations are intended as examples ofthe present inventive concept and are not to be construed as limitationsthereof. Still other variations and rearrangements of parts within thespirit and scope of this invention are possible and will presentthemselves to those skilled in the art.

I claim:
 1. A disposable canister for use in a humidifier assembly forhumidifying a breathable gas to be inhaled by a patient undergoinginhalation therapy; said humidifier assembly including a heater meansmounted on a housing and having an exposed heated surface adapted toreceive liquid water in direct heat transfer relationship therewith, andliquid water supply means for the exposed heated surface; and saidcanister comprisinga hollow shell having an open end adapted forremovably mounting on said housing and provided with a gas inlet and agas outlet; and a porous, vapor-permeable but hydrophobic filtermembrane mounted within said hollow shell across said open end but at aposition substantially uniformly spaced from said open end and saidexposed heated surface when the shell is mounted on said housing; saidhollow shell together with said hydrophobic filter membrane togetherdefining a humidification chamber on one side of the filter membranethat communicates with the gas inlet and the gas outlet in the shell andthrough which said breathable gas is adapted to pass between the inletand the outlet, and defining a heater-receiving cavity on the other sideof the filter membrane.
 2. The disposable canister in accordance withclaim 1 wherein the porous, water vapor-permeable portion has a poresize of about 0.02 to about 0.5 micrometers.
 3. The disposable canisterin accordance with claim 1 wherein said humidification chamber isprovided with a vent.
 4. The disposable canister in accordance withclaim 3 wherein the vent includes a hydrophobic filter element.
 5. Thedisposable canister in accordance with claim 1 further including a baseassembly for the canister adapted for removable positioning over theheater means; said base assembly including a projecting nipple foractuating a valve on said heater means.
 6. The disposable canister inaccordance with claim 1 wherein the hydrophobic filter membrane is amicroporous expanded polytetrafluoroethylene structure having a matrixof nodules interconnected with fibrils and has a pore size of about 0.02to about 0.5 micrometers.